Conventional telephone sets include as part of their equipment a ringer device or "ringer" which is separate from the other components of the set. The ringer is, together with associated ringer circuits, mounted on the base of the set and coupled to the telephone lines when the set is "on-hook" (i.e., the handset is resting in the cradle) so that the switch hook disconnects the handset from the lines. When a ringing signal is received from the central office, the ringer circuits respond thereto to supply to the ringer an electrical signal which is converted by the ringer into sound tones alerting the telephone subscriber that he or she is being called.
The ringer is, however, an item of expense in a telephone set. Accordingly, various proposals have been made to eliminate the ringer by using another component of the set to perform its regular function during voice mode operation of the set and, also, to provide the ringing sound when the set is in its ringing mode of operation. Thus, for example, U.S. Pat. No. 4,251,694 issued Feb. 17, 1981 in the name of Raymond G. Taylor and incorporated herein by reference discloses a telephone set having the usual base, cradle, switch hook and handset but which is arranged so that, while the telephone is "on-hook," a ringing signal from the central office actuates the handset receiver to produce a ringing sound. In connection with such an arrangement, however, the danger arises that, if a telephone user should hold the handset to his/her ear and then manually depress the cradle to put the set in "on-hook" condition, a ringing signal from the central office will be converted by the handset receiver into a ringing tone which may damage the ear of the user. To forestall such danger, the Taylor set includes a protective device which senses the presence or absence of the handset in the cradle whether it is depressed or not, and which permits the ringing tone to be produced by the handset receiver only when such device senses that the handset is indeed in its cradle.
While the Taylor set represents a significant advance in the art, it has the disadvantage that it requires the mentioned protective device which is an item of expense. Moreover, the arrangement disclosed in the Taylor patent is not adapted for use in a switch-hookless telephone set.